Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
This code means there is a problem with the part of the car that controls how much fuel goes into the engine for cylinder 11. It's like a light switch that's stuck in the off position, so the fuel can't get through properly.
The code indicates that the low side circuit for the hydrogen injector in cylinder 11 is experiencing low voltage or is not functioning correctly.
The P31AC code is triggered when the Engine Control Module (ECM) detects a low voltage condition in the low side circuit of the hydrogen injector for cylinder 11. This could be due to a wiring issue, a faulty injector, or a problem with the ECM itself.
• Engine misfire
• Reduced engine performance
• Check Engine Light illuminated
• Faulty hydrogen injector
• Damaged wiring or connectors
• Faulty Engine Control Module (ECM)
ECM: Engine Control Module, the computer that controls the engine's functions.
Injector: A device that sprays fuel into the engine's cylinders.
• Perform a visual inspection of the injector and wiring.
• Use a multimeter to check for voltage at the injector.
• Test the ECM for proper operation.
• Replace the faulty hydrogen injector.
• Repair or replace damaged wiring or connectors.
• Replace the ECM if necessary.
• Multimeter
• OBD-II scanner
• Basic hand tools
$200 - $600
Moderate
• Vehicle 1
• Vehicle 2
• Vehicle 3
• Regularly inspect wiring and connectors.
• Perform routine maintenance on the fuel system.
• Keep the ECM updated with the latest software.
Engine Performance
• Do not ignore the Check Engine Light.
• Have the vehicle inspected by a professional mechanic.
• Avoid driving the vehicle aggressively until the issue is resolved.
Check with your vehicle manufacturer for warranty coverage on emissions-related components.
This code is relatively uncommon and is typically associated with vehicles using alternative fuel systems.
Moderate – It should be addressed soon to avoid potential engine damage.
Driving with a malfunctioning injector can lead to increased emissions and potential engine damage.
• Engine at operating temperature
• Vehicle in a safe, stationary position
The hydrogen injector for cylinder 11 is located on the engine block, typically near the intake manifold.
Q: Can I drive my car with this code?
A: It's not recommended to drive for extended periods with this code, as it can lead to engine damage.
Q: How can I reset the Check Engine Light?
A: You can reset the light using an OBD-II scanner after the issue is fixed, but it may come back if the problem persists.
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Universal · Digital multimeter
A solid entry-level multimeter for voltage, continuity, resistance, and basic electrical troubleshooting.
Helpful for checking voltage drops, grounds, and basic circuit health when modules are not communicating.
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Useful when diagnosis points toward damaged wiring, corroded terminals, or connector repairs.
Useful if diagnosis points toward damaged connectors, wiring, or terminal repairs.
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Fitment Required · Vehicle-fitment part
Commonly relevant for misfire, ignition-efficiency, and some drivability-related repairs.
Misfire and ignition-related faults commonly involve spark plugs as part of the repair path.
Check the correct plug type, gap, and engine application for your vehicle.
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Fitment Required · Vehicle-fitment part
Relevant when the fault points toward ignition-coil performance or cylinder-specific ignition issues.
Some ignition faults involve coil performance or cylinder-specific coil problems.
Match the coil to your engine and confirm the failed component before ordering.
View options on AmazonThese parts may be related to this fault category, but a code by itself does not confirm exact fitment or guarantee that replacing a part will solve the problem.